Meibomian glands, which are positioned throughout the eyelid margins, provide lipid like secretions (known as meibum) to the surface of the eye. When blinking occurs, the upper eyelid moves downwardly over the eye and assists the lipid secretion between the margins of the eyelids. Upon eye opening, the upper lid moves upwardly and pulls a sheet of lipid upwardly to form a film over the eye. This lipid sheet coats the aqueous part of the tear layer which in turn coats the surface of the eye. The presence of this lipid sheet restricts evaporation of the tear layer such that the surface of the eye is maintained in a moist environment. Failure of the meibomian glands will mean that the required lipid layer is not properly formed and evaporation of the tear layer will occur rapidly which will lead to sensations of dryness, irritation and burning.
The main cause of failure of the meibomian glands is due to their becoming clogged. A number of factors may lead to clogging. For example, hormonal changes, particularly in levels of oestrogen, can result in thickening of the oils which will in turn clog the glands. In addition, it has been suggested that changes in oestrogen levels may cause staphylococcal bacteria, which naturally inhabit the eye, to proliferate. Unfortunately, this proliferation may cause the bacteria to invade the meibomian glands which can cause a decrease in the secretion of lipids from the glands.
Additionally or alternatively the clogging may be caused by immunological factors such as sebhorreic blepharitis or systemic diseases such as acne rosacae. Blepharitis also affects the lid margin and is often associated with meibomian gland dysfunction. Blepharitis occurs in increasing prevalence with the age of the patient. Where blepharitis occurs, inflammation of the lid margins may be noted often in combination with redness. In addition, scales, crusts and/or marginal ulcers may be observed.
Mechanical failure may also cause the glands to dysfunction. Further information relating to the aetiology of meibomian gland dysfunction may be found in Gutgessel V J et al (1982) Histopathology of Meibomian Gland Dysfunction. Ma. J. Opthal 94: 383-388.
An increased disfunction of the meibomian gland is noted with age and in addition may be seen to be higher in contact lens wearers. In Ong B L and Lark J R (1990) Meibomian Gland Dysfunction: Some Chemical, Biochemical and Physical Observations, Opthal: Physiol Opt 10: 144-148 a 30% prevalence of gland dysfunction was noted in contact lens wearers and 23% in non-contact lens wearers in a preliminary study involving 140 subjects, half of which were contact lens wearers.
In Ong B L (1996) “Relation Between Contact Lens Wear and Meibomian Gland Dysfunction” Optom & Vis Sci 73: 208-210, 231 subjects were evaluation of which 81 were contact lens wearers. A prevalence to meibomian gland dysfunction was noted in 43% of the contact lens wearers and 35% of the non-contact lens wearers.
The effect of age was considered by Hom M M et al in “Prevalence of Meibomian Gland Dysfunction 1990 Optom & Vis Sci 67: 710-712. Here 298 patients aged from 10 to over 60 were tested. The results reported an overall prevalence to dysfunction of 39%. However, the levels were low at a young age with a marked increase being noted as age increased. For each decade up to 49 years there was an increase with the maximum being at 40%. From 50 to 59 years a prevalence of 51% was noted, and for patients over 60, the prevalence was noted to have risen to greater than 67%.
In addition to contact lens wearing and aging, abnormal behaviour of the meibomian glands may be exacerbated by illness or the use of cosmetics.
The severity of meibomian gland dysfunction is variable and depends on the stages of the dysfunction. In the initial stages increased secretion is noted. This leads to over development of the epithelial cells lining the duct of the glands and to modification of the lipid composition. These cells may be excreted from the glands producing dandruff-like scales.
In the intermediate stage, the change in lipid composition leads to an increase in the melting point of the lipid, such that it becomes a paste like solid at eyelid temperature which leads to partial or total blockage of the meibomian glands. The further production and accumulation of desquamated epithelial cells adds to the blockage of the gland orifices.
In the advanced stages, long term blockage of the glands can lead to the meibomian glands becoming atrophied. It is essential to commence treatment before the final stage is reached since once the glands have become atrophic, the dysfunction is irreversible.
The slow evolutionary nature of the dysfunction means that the stages of meibomian gland dysfunction is often different for different glands along the same eyelid margin.
Conventionally, the blocked glands are treated with a cloth, facecloth or towel which is immersed in boiling water, allowed to partially cool and then placed over closed eyes. The aim of the treatment is to melt the solidified lipids and to loosen the debris which has collected around the glands and at the base of the eyelashes. It is sometimes suggested that salt should be applied to the cloth.
Whilst this treatment may be effective if correctly performed, it does suffer from certain disadvantages and drawbacks. The main drawback is that the user must estimate when the cloth is at the correct temperature before placing it over the eyes. If the cloth is too hot, there is a risk that the patient will be scalded. Conversely, if the cloth has cooled too much, the treatment will be ineffective. Further, it is a cumbersome and awkward treatment which cannot readily be utilised outside of the home. Since the procedure is complex and time consuming it is often abandoned by the patient before the required benefits are obtained. A further disadvantage of this method is that even if the cloth is at the correct temperature at the start of the treatment, it will rapidly cool such that the required temperature is only maintained for a short period of time.
An additional drawback is that there is a risk of bacterial contamination as the cloth is not sterile. This is a particularly serious problem for contact lens wearers.
A second stage of treatment is to treat the eyelid margin with cleaning agents. Examples of suitable cleaning agents are those sold under the trade marks “Lid-Care” by CibaVision and “Supranettes” by Alcon.
Whilst the use of hot cloths and cleaning agents may go some way to addressing the symptoms of meibomian gland dysfunction, there is still a need for a treatment system which will overcome the above-mentioned disadvantages and which can be readily used by patients with busy lifestyles.
Other eye problems may benefit from treatment with a hot wipe or in some circumstances with a cooled wipe. These problems include the eye symptoms encountered by hayfever sufferers and the swelling/edema caused by trauma. The application of a cooled wipe to the eye region may also be beneficial in the treatment of headaches. It is recommended that, for example for the treatment of swelling, cooling with cold water at about 8° C. for about 30 minutes is recommended. Although for ice therapy the application time may be significantly shorter. Conventionally, where the extreme treatment in which ice is applied it is necessary to take extra care to ensure that ice is not applied directly to the skin since burning can occur.